We will use pentobarbital anesthetized dogs on cardiopulmonary bypass for two studies of central airway reflexes to be performed under conditions of maximum isolation of interacting control systems. The first study is an attempt to discern the potential role of primary vascular events on respiratory mechanics. In it we will seek influences on central airway motor tone brought about by distention of pulmonary vessels and left heart chambers, by systemic arterial baroreflexes, and by stimulation of pulmonary type-J receptors. Changes in extraparenchymal airways will be compared with changes in airway resistance and dynamic lung compliance. The second study is directed at resolving the controversy concerning the roles of central and peripheral airway stretch receptors in the control of breathing. We will compare the individual influences of central airway and peripheral lung distention on electrical activity of the diaphragm under two conditions, namely, when the lung volume changes tidaly with respiratory muscle activity and when it does not. We predict that central airway stretch receptors may be important in the control of breathing only when associated lung volume changes occur and that peripheral stretch receptors have a different inhibitory influence on central rhythm generation, most apparent when lung volume changes and breathing activity are decoupled.